The invention relates to a process for covering, in a quasi-hermetic manner that is low in reactive effects, susceptible physical structures on structure-backing surfaces to protect against soiling, chemical actions and/or physical degradations.
In practice, a problem is incurred with respect to many high-precision, microelectronic, physical, medicinal, chemical components and elements, namely how to screen functional structures deposited on the surface so they are protected to a very high degree against the actions from corrosive, aggressive and structure-deforming chemical components of the environment or against the penetration of, or exchange with, gaseous or vaporous and also liquid atmospheric ingredients.
Many methods are presently known to achieve approximately "hermetic" seals for solving many of such problems. Representatively, though not exclusively, the following are listed below:
(a) metallic covers which are metallically welded or soldered to a metal structure-backing, though they also may be bonded in special cases by organic, and, better yet, inorganic cements, PA1 (b) glass and ceramic covers which are fused or bonded with the structure backing, PA1 (c) galvanic coatings, PA1 (d) oxide coatings, PA1 (e) metal oxide or ceramic coatings deposited in vacuum for instance by sputtering or evaporation methods, and PA1 (f) epitaxial layers.
Provided sharp restrictions on sealing quality are accepted, it is also possible to use coverings of organic enamels, foils, paints or molded parts.
However, even if these do evince high chemical resistance and excellent liquid-repelling, in particular hydrophobic, properties they can seal the structures only incompletely over the long term against gases and vapors of low molecular weight because these organic covering substances ordinarily comprise cross-linked macromolecular structures which amount to molecular filters for the mentioned gases.
Typical examples are the casings for integrated semiconductor circuits and components:
The widely used plastic casings in spite of their relatively thick-walled coverings offer only restricted protection against water vapor and other structurally degrading gases; long-term stability (mil-designs) are ensured only by metal cases and those made of ceramics (Al.sub.2 O.sub.3, etc.).
The selection among technically suitable solutions is much restricted when there is a need for the covering providing both the most hermetic possible seal, and that it affect the functional properties of the structure support, and/or of the structure itself as little as possible.
Thus, it may be necessary to minimally modify the heat capacity, the heat transfer, the mass of the geometric size of the structure support and/or of the structure itself by the deposition of the covering, or there may be a requirement of unimpeded access of radioactive, electromagnetic (light) or acoustic irradiation to the structure.
The term "structures" as employed herein relates preferably to such sensor elements and electrical networks as photodiodes, resistors with positive or negative temperature coefficients, gaussian elements, coils, capacitor coatings, resistance networks made from foils, wires and thin films and consisting of metal or semiconducting materials, though there are many others, which must meet high requirements in long-term stability and reproducibility.
An important illustrative application is provided by precision pick-ups for forces, pressures, and torques, among others, which by means of strain-sensing devices, for instance strain gauges, SAW generators, or capacitive pick-ups convert the surface expansions of particular surface zones of measuring springs as structure supports into electrically useful signals as a function of the mechanical values cited above that are to be measured and which are experienced by the measuring springs.
It is the object of the present invention to provide a process to cover such strain gauge strips, and further also all otherwise similar structures deposited on the surface on which they are operative, in a highly effective manner without thereby affecting the operation thereof.